A convenient synthesis of some new substituted 3,5- dimethyl pyrazole (4a-c), 3-methyl pyrazol-5-one derivatives (5a-c), 3-Methyl-1-(substituted phenyl) pyrazol-5-ones (7a-b) and 2,3-dimethyl-1-(substituted phenyl)pyrazol-5-ones (8a-b) have been synthesized. All the newly synthesized compounds were tested for their in vivo anti-inflammatory and analgesic activity by bioassays namely: Carrageenan-induced paw edema method and acetic acid induced writhing method respectively. All the synthesized compounds have been characterized by their melting point, elemental analysis, IR and 1H-NMR. Compound 8b exhibited promising and significant inhibitory activity against COX-2 enzyme. Therefore, such compounds would represent a fruitful matrix for the development of anti-inflammatory and analgesic agents.